by Kim Skibbe, DVM
When a dog is diagnosed with dilated cardiomyopathy (DCM), the type and cause can vary from confirmed diet-associated DCM to suspected diet-associated DCM, genetic and breed-specific DCM, or DCM of unknown cause.
In our Facebook group, we receive many questions about how a case of DCM is confirmed to be diet-associated. These questions are a good opportunity to discuss diagnostic differentials versus a confirmed diagnosis versus proof of diet-associated DCM.
Ultimately, the diagnostic terms are suspected, confirmed, proven and open.
Diagnosis of any illness is based on an abundance of evidence
In dogs, an evidence-based diagnosis involves many factors:
- Signalment: breed, age, sex
- History: diet, environment, exercise, previous health problems, owner reported-symptoms
- Physical exam results
- Imaging results
- Laboratory testing results
A diagnosis is not the same as proof
Here’s an example of why a diagnosis is not always proof of the cause of an illness…
If I have a dog with a positive parvovirus test, was not vaccinated for parvovirus, has severe vomiting and diarrhea, and is treated and recovers – it is appropriate for me as a medical professional to diagnose this dog with parvovirus. But this is not proof. We did not do an intestinal biopsy to isolate the virus, and we did not prove the dog did not eat garbage before his diagnosis, so it is simply not feasible or appropriate to claim proof of the diagnosis.
Medical professionals consider all differentials of a case. We then move to a ‘working’ or ‘suspect’ diagnosis, and arrive at a ‘confirmed’ or ‘proven’ diagnosis when evidence becomes clearer. If we are very uncertain about a diagnosis, it is called ‘open.’
So back to DCM
Veterinary cardiologists are most qualified to diagnose DCM. They do this largely based on echocardiogram imaging (ultrasound of the heart). When results do not lend themselves to a firm diagnosis, cardiologists may call it something like ‘equivocal for DCM’ or ‘suspected DCM.’
Let’s suppose the cardiologist is comfortable with a DCM diagnosis. This is now ‘confirmed DCM.’ Once confirmed, how do we know if DCM is diet-associated? First, based on the cardiologist’s current knowledge, as well as the dog’s history and signalment, the cardiologist can strongly suspect a diet-associated cause.
The more cases correlated with diet, the more we understand the role of diet in DCM. As of November 2019, there were two peer-reviewed papers documenting improvement when dogs with confirmed DCM were switched to quality, proven diets. Many more studies are under way, and our observations of dogs diagnosed with DCM that are improving or completely recovering with a change of diet continue to validate the role of diet in DCM.
Here are considerations in which history and signalment help determine the type of DCM:
- If your dog is a Doberman Pinscher with DCM and your dog has been fed a quality and proven diet, the working diagnosis is probably going to be genetic DCM, given this breed’s genetic predisposition to DCM.
- If your dog is a Labrador Retriever fed a grain-free diet, particularly from a company that does not meet global nutrition guidelines established by the World Small Animal Veterinary Association (WSAVA), the presumptive diagnosis might be ‘suspected diet-associated,’ given this breed is not genetically predisposed to DCM. Some professionals might also call this a ‘working diagnosis.’
- If you have a breed susceptible to genetic DCM but there is no DCM history in the lineage – AND your dog has been eating a suspect diet, a cardiologist may not at first attribute it to either diet-associated or genetic DCM.
When does a case of DCM become confirmed as diet-associated?
Cardiologists are able to confirm diet-associated DCM when there is also a taurine deficiency OR when the dog improves after diet change (or both), indicated by echocardiographic evidence of improvement.
Sadly, some cases are too advanced when diagnosed, thus a dog’s heart is not able to improve with diet change and medical intervention. In these cases, cardiologists may have to look at overall data, including the occurrence of genetic DCM in the breed (dogs with genetic DCM do not improve), as well as the occurrence of diet-associated DCM with the dog’s particular diet. With these and other observations in mind, cardiologists can offer opinions on whether a case is likely diet-associated or genetic.
That said, the more evidence collected on certain diets correlating with DCM, the more likely it is that a DCM dog fed those diets has diet-associated DCM. Our Facebook group has members submit cardiology reports for their dogs with DCM, and the implicated brands chart we maintain bears resemblance to data collected by the U.S. Food and Drug Administration (FDA).
Many pet food manufacturers claim there is no proof that their food causes DCM. Of course, there is no proof because we cannot read the minds of myocardial cells or retrieve recorded histories of them saying they were damaged by diet. We can, however, use medical and scientific evidence to identify certain diets as a causative factor in canine DCM. So, if a manufacturer tells you there is no proof, you might want to turn the conversation to ‘evidence’ – even a ‘growing body of evidence’ – that connects their food to diet-associated DCM.
Explore this website for more information, and join our Facebook group to stay up to date on canine diet-associated DCM: